The gaseous mixture produced in the regenerator of fluid catalytic cracking process systems contains solid particulates, including catalyst fines, and acidic gases, such as, sulfur oxides. It is desirable to lower the level of solid particulates and acidic gases from such a gas before it is introduced into the atmosphere so as to minimize the detrimental effect of these pollutants to the ecology. It is known that solid particulates can be removed from gases by wet scrubbing methods including scrubbing gases in jet ejector type venturi scrubbers in which a scrubbing liquid, under pressure, enters the venturi through a spray nozzle. The velocity of the liquid spray creates a draft in a chamber of the venturi scrubber and causes gases or vapors to be drawn into the scrubber body and through a constricted passage of the scrubber wherein intimate mixing of scrubbing liquid and gas occurs. Generally, the effluent of the scrubber (which may be one or more venturi structures in series or in parallel) is passed to a separator in which the contaminated liquid is separated from the cleaned gas. It is also known that acidic or basic materials may be added to the scrubbing liquid to neutralize or absorb basic or acidic contaminants that may be present in the gas subjected to the wet scrubbing treatment.
Although many types of venturi wet gas scrubbing systems have been proposed to reduce the level of particulates and acidic gases from gaseous mixtures prior to their discharge to the atmosphere, the suitability of any specific wet scrubbing system for the efficient removal of solid particulates and other contaminants from gaseous mixtures has been difficult to predict. The nature of the carrier gas, the nature and size of the solid particulate contaminants and the nature of the pollutant gas are factors which will affect the operability and efficiency of removal of contaminants by the known venturi wet gas scrubbing methods.
Heretofore, it has been found that solid particulates, including cracking catalyst fines, condensable contaminants and acidic gases, such as, sulfur oxides, can be reduced to an appropriate level in the gaseous mixture that has been produced in the regenerator unit of a fluid catalytic cracking system by a wet gas scrubbing process carried out under specified conditions, utilizing a jet ejector type of venturi scrubber. Such a method has been disclosed in U.S. Pat. No. 3,970,740 by Reeder and Williams, issued July 20, 1976 and entitled "Wet Scrubbing Process", which is incorporated by reference herein.
The process of U.S. Pat. No. 3,970,470 proved effective in industrial applications to remove from 85 to 90% of the catalyst fines present in the regenerator off gas of a fluid catalytic cracking system and to remove up to 95% of sulfur dioxide present in the off gas. It is anticipated, however, that sulfur dioxide emissions will be even more stringently controlled in the future. Accordingly, there is a need in the industry for an improved process to effectively removing both catalyst particulates and more than 95% of sulfur oxides in the regenerator effluent gas of a cat cracking system. The primary objective of this invention is to fulfill this need.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.